I'd suggest looking for industrial motherboards. I'm not really sure there is such a thing as industrial GPU's:
Industrial Motherboards for form factor from mini-ITX, thin mini-ITX, 3.5" Single Board Computer (SBC) to Smart Display Module (SDM), perfectly suits applications in POS, KIOSK, vending machine, digital signage, healthcare, industrial automation, IoT, edge computing, etc.
www.gigabyte.com
Typically they use derated components, that's about it, in a simplified design. It's really going to be how you assemble the system that makes it "rugged". After initial assembly and test out, I'd stake all heavy components on the motherboard and in the GPU with an appropriate epoxy adhesve (3M 2216 b/a is perfect for this).
Probably fabricate some support frames for mounting and supporting the GPU connected with a PCie extender cable. CPU cooling can be a problem since coolers also have to be properly shock supported; you don't want them bouncing around on top of the CPU as you go down the road. Also give the chassis some really good cooling air flow, with filtration using something like an automotive intake air filter, not typical PC chassis filters, to keep road dust out. I'd also derate the CPU and GPU clocks so they run cooler, if you can.
I'd also be very concerned about the PSU you use; I'm really not sure I've seen any ruggedized PSU's so you may have to get inside and stake the crap out of everything with that 2216 b/a. Cars move and vibrate incessantly, shocks and vibrations tear up delicate electronics. Heavy parts don't like to stop when the car stops or hits bumps so it tears at solder joints with time. Do that sort of thing accompanied with vibrations and thermal cycles and they crack. That's why you have to stake parts to the PWB or you'll soon be chasing gremlins.